Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J155/00—Adhesives based on homopolymers or copolymers, obtained by polymerisation reactions only involving carbon-to-carbon unsaturated bonds, not provided for in groups C09J123/00 - C09J153/00
  • C09J155/005—Homopolymers or copolymers obtained by polymerisation of macromolecular compounds terminated by a carbon-to-carbon double bond
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
  • C09J133/04—Homopolymers or copolymers of esters
  • C09J133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
  • C09J133/08—Homopolymers or copolymers of acrylic acid esters
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J7/00—Adhesives in the form of films or foils
  • C09J7/30—Adhesives in the form of films or foils characterised by the adhesive composition
  • C09J7/38—Pressure-sensitive adhesives [PSA]
  • C09J7/381—Pressure-sensitive adhesives [PSA] based on macromolecular compounds obtained by reactions involving only carbon-to-carbon unsaturated bonds
  • C09J7/385—Acrylic polymers
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J2301/00—Additional features of adhesives in the form of films or foils
  • C09J2301/30—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier
  • C09J2301/302—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier the adhesive being pressure-sensitive, i.e. tacky at temperatures inferior to 30°C

Definitions

• the present invention relates to a novel blister-­free pressure-sensitive adhesive sheet. More particularly, the present invention relates to a pressure-sensitive adhesive sheet which can be applied and bonded to the surface of shaped articles of various kinds of plastic resins without occurrence of blisters.
• pressure-sensitive adhesive sheets having a coating layer of a pressure-sensitive adhesive are widely used and now indispensable in a variety of industrial fields, for example, as a printed label, seal on wrapped packages and the like. This is because pressure-sensitive adhesive sheets can be readily bonded to the surface of various substrates conveniently by merely putting on and lightly pressing to the substrate surface and, different from adhesives in general, the pressure-sensitive adhesive forming the coating layer of the sheet contains no organic solvent so that no problems of environmental pollution are caused thereby advantageously.
• Pressure-sensitive adhesive sheets can be applied and bonded to the surface of a substrate article of any materials almost without limitation including paper, wood, metals, ceramics, plastics and the like.
• a transparent pressure-­sensitive adhesive sheet used in such an application has a printed pattern as desired, the plastic-made article to which such a sheet is attached on the surface may have an outer appearance as if it were printed directly thereon.
• pressure-sensitive adhesive sheets are sometimes attached to the surface of a board of polycarbonate resins used as a window pane by virtue of the high transparency with an object to protect the surface from scratches or to control transmission of sun light therethrough.
• Pressure-sensitive adhesive sheets in general have a serious problem that, when an adhesive sheet is applied and bonded to the surface of an article made of polystyrene resin, polycarbonate resin and the like, so-called blisters are not rarely formed due to incomplete squeeze-out of the air between the substrate surface and adhesive sheet attached as a label or a protecting sheet.
• This problem is unavoidable when the face-stock film of the pressure-­sensitive adhesive sheet is made of a plastic resin having gas barrier property such as conventional polyester resins.
• One of the possible means to solve this problem by dissipating the gas in the blisters is to provide a gas-­permeable layer made of paper, porous polyurethane and the like between the face-stock film and the adhesive coating layer of the pressure-sensitive adhesive sheet.
• This method has no general applicability because the overall thickness of the adhesive sheet is necessarily increased so much and the adhesive sheet can no longer be used as a see-­through label due to the loss of transparency by the interposed gas-permeable layer.
• the present invention accordingly has an object to provide an improved blister-free pressure-sensitive adhesive sheet free from the above described problems and disadvantages in the conventional pressure-sensitive adhesive sheets, which has excellent characteristics that the adhesive layer is highly resistant against weathering with excellent retention of adhesiveness of that of blisters can effectively be prevented when the adhesive sheet is applied and bonded to the surface of a substrate even without providing the above mentioned gas-permeable layer between the substrate and the adhesive layer.
• the pressure-sensitive adhesive sheet of the present invention comprises:
• the most characteristic feature of the inventive pressure-sensitive adhesive sheet consists in the very unique pressure-sensitive adhesive composition forming the coating layer on the face-stock film and comprising, as the principal ingredient, a copolymer having a specified molecular weight and a specified glass transition temperature and composed of three types of monomeric moieties each in a specified weight fraction.
• the invention has been completed as a result of the extensive investigations undertaken with an object to develop a pressure-sensitive adhesive sheet outstandingly free from the disadvantage of blisters leading to a discovery that the polymeric molecular chain of the moiety of the macromonomer introduced into the copolymer as the pendant groups may act to absorb any trace volume of gases emitted from inside of the resinous substrate and responsible for the formation of blisters so that of blisters can be efficiently prevented and the adhesive sheet can exhibit excellent adhesion and retention of adhesiveness to achieve the above described object of the present invention.
• the pressure-sensitive adhesive sheet of the present invention basically has a structure in which a coating layer of a pressure-sensitive adhesive composition is provided on the surface of a face-stock film which may be colored or provided with a thin vapor-deposited or sputtered film of a metal, e.g., aluminum, when control of sum light trans­mission is desired although it is also possible to use a colored pressure-sensitive adhesive.
• a coating layer of a pressure-sensitive adhesive composition is provided on the surface of a face-stock film which may be colored or provided with a thin vapor-deposited or sputtered film of a metal, e.g., aluminum, when control of sum light trans­mission is desired although it is also possible to use a colored pressure-sensitive adhesive.
• the principal ingredi­ent of the pressure-sensitive adhesive composition is a copolymer composed of (a) a first monomeric moiety of an acrylic ester, (b) a second monomeric moiety of an acrylic compound having a polar group in the molecular structure and (c) a third monomeric moiety of a macromonomer compound having a polymeric molecular chain and a polymerizable functional group at the molecular chain end.
• the first monomeric moiety (a) of an acrylic ester is exemplified by the moieties of alkyl esters of acrylic acid or methacrylic acid of which the alkyl group has 1 to 14 carbon atoms.
• the acrylic ester monomers from which the first monomeric moiety is derived include esters of acrylic or methacrylic acid with an alcohol having 1 to 14 carbon atoms in a molecule such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, n-pentyl alcohol, pentan-2-ol, pentan-3-ol, 2-methyl butan-1-ol, 3-methyl butan-1-ol, hexan-­2-ol, 2-methyl pentan-1-ol, 3-methyl pentan-1-ol, 2-ethyl butan-1-ol, 3,5,5-trimethyl hexan-1-ol, heptan-3-ol,
• the second monomeric moiety (b) is derived from an acrylic compound having a polar group in the molecular structure.
• the polar group here implied includes carboxyl group, hydroxy group, amino group, amido group, epoxy group, cyano group, isocyanato group and the like.
• the acrylic compound may have two kinds or more of these polar groups in a molecule.
• acrylic compound having a polar group examples include (meth)acrylic acid, 2-hydroxyethyl (meth)-­acrylate, 2-aminoethyl (meth)acrylate, (meth)acrylamide, glycidyl (meth)acrylate, (meth)acrylonitrile, 2-isocyano­ethyl (meth)acrylate, itaconic acid, maleic acid and the like.
• the polar group or groups should be the pendant groups to the polymeric molecular chain.
• the third monomeric moiety (c) is derived from a macromonomer and has a polymeric chain and polymerizable functional group at the molecular chain end.
• the polymeric chain is composed of the moiety of styrene, methyl methacrylate or a copolymeric moiety of styrene or methyl methacrylate with a minor amount of acrylonitrile or vinyl acetate.
• the polymeric chain preferably has a molecular weight in the range from 1000 to 30,000 and a glass transition temperature of 30°C or higher.
• the polymerizable functional group is not particularly limited insofar as it can be with or incorporated in the above described acrylic ester monomer and the polar acrylic monomer. Examples of suitable copolymerizable functional group include meth­acryloyl group, allyl group, vinyl benzyl group and the like.
• the copolymer thus obtained is a graft copolymer having the polymeric chains of the macromonomer as the pendant groups to the polymeric main chain.
• the polymeric chains as the pendant groups of the copolymer serve to prevent occurrence of blisters in the pressure-sensitive adhesive sheet by absorbing any trace volume of gases emitted from the resinous substrate.
• the above mentioned macromonomer can be prepared by a variety of known methods without particular limitations.
• Applicable methods include, firstly, a method in which methacryloyl chloride or the like is reacted with living polymer anions prepared in advance for forming the polymeric chain portion of the macromonomer, secondly, a method an oligomer having carboxyl groups at the molecular chain terminals is prepared by the oligomerization of a radical-­polymerizable monomer such as methyl methacrylate in the presence of mercapto acetic acid as a chain transfer agent and the oligomer is then converted into a macromonomer by the reaction with glycidyl methacrylate, thirdly, a method in which an oligomer having hydroxy groups at the molecular chain ends is prepared by using 2-mercaptoethyl alcohol as a chain transfer agent and then the oligomer is converted into a macromonomer by the reaction with 2-hydroxyetyl meth­acrylate,
• the above described copolymer is composed of the three types of the monomeric moieties each in a specific weight fraction such that the weight fractions of the first monomeric moiety (a) of the acrylic ester, the second monomeric moiety (b) of the polar acrylic monomer and the third monomeric moiety (c) of the macromonomer are in the range from 50 to 85% by weight, from 1 to 30% by weight and from 5 to 40% by weight, respectively, with the proviso that the weight ratio of the second monomeric moiety (b) to the third monomeric moiety (c) is in the range from 0.02 to 6.
• the weight fraction of each of the three monomeric moieties is outside of the above mentioned range, the copolymer is not suffi­ciently effective to prevent blistering of the pressure-­sensitive adhesive sheet or cannot exhibit high adhesive performance.
• the copolymer used in the inventive pressure-­sensitive adhesive sheet should have a weight-average molecular weight in the range from 150,000 to 2,000,000 or, preferably, from 250,000 to 1,500,000 or, more preferably, from 300,000 to 1,000,000.
• a weight-average molecular weight of the copolymer smaller than 150,000 is undesirable due the eventual poor holding power of adhesiveness of the copolymer.
• a weight-average molecular weight larger than 2,000,000, on the other hand, is also undesirable in respect of the poor workability in the coating.
• the copolymer should have a glass transition temperature in the range from -60 °C to +60 °C or, preferably, from -30 °C to +20 °C.
• the glass transition temperature of the copolymer is lower than -60 °C, the pressure-sensitive adhesive sheet hardly has a sufficiently high adhesive bond strength.
• the glass transition temperature thereof exceeds +60 °C, on the other hand, the ball-tack of the adhesive sheet may be decreased as a trend.
• the copolymer used in the inventive pressure-­sensitive adhesive sheet can be prepared by any of known methods including the following three methods. Firstly, copolymerization of the three monomers is performed simul­taneously by admixing a radical polymerization initiator such as azobisisobutyronitrile with a mixture of an acrylic ester monomer, a polar acrylic monomer and a macromonomer having a polymeric molecular chain and a polymerizable functional group at the molecular chain end to start the copolymerization reaction.
• a radical polymerization initiator such as azobisisobutyronitrile
• an acrylic ester monomer and a polar acrylic monomer having a reactive group such as a carboxyl group and hydroxy group are first copolymerized to give a copolymer having reactive groups at the pendant groups followed by the reaction thereof with macrosegments composed of polymeric molecular chain having a reactive group capable of being bonded with the above mentioned reactive groups in the copolymer such as an isocyanate group, hydroxy group, carboxy group and the like.
• a monomer having a reactive group capable of initiating grafting reaction such as a polymerizable organic peroxide, an acrylic ester monomer and a polar acrylic monomer are copolymerized to give a copolymer which is then subjected to a graft-copolymerization reaction with a grafting monomer such as styrene, methyl methacrylate, acrylonitrile and the like.
• the copolymers obtained by these methods have a final structure identical with that of the copolymer prepared by the first method so that they can be used as the copolymer according to the present invention.
• the desired blister-preventing effect as the object of the present invention cannot be obtained when the above described copolymer is replaced with a copolymer prepared by the copolymerization of an ethylenically unsaturated monomer such as styrene, methyl methacrylate and the like with and other monomers for the nomomeric moieties (a) and (b) having the moiety of styrene of methyl methacrylate as the units forming the main chain of the copolymer or replaced with a polymer blend composed of a polymer such as polystyrene, poly(methyl methacrylate) and the like and a copolymer of an acrylic ester monomer and a polar acrylic monomer.
• the pressure-sensitive adhesive sheet of the present invention can be prepared by coating a surface of a face-­stock film with the pressure-sensitive adhesive composition mainly composed of the copolymer obtained in the above described manner according to a coating method conven­tionally used in the manufacture of adhesive sheets. It is optional according to need that the adhesive composition is admixed with aging retarders such as ultraviolet absorbers, antioxidants and the like to enhance the durability of the adhesive sheet.
• aging retarders such as ultraviolet absorbers, antioxidants and the like to enhance the durability of the adhesive sheet.
• the type of the base sheet to be coated with the adhesive composition is not particularly limitative including films and sheets of a synthetic resin such as polyester, poly(vinyl chloride), polypropylene, polyethy­lene, polyurethane and the like, synthetic paper, cellulose-­based films and sheets, woven and non-woven cloths as well as knit cloths of various kinds of materials and so on. If desired, these base sheets can be printed to exhibit suitable patterns such as characters and marks on the surface not coated with the pressure-sensitive adhesive to meet the particular application of the adhesive sheet.
• the coating layer of the pressure-sensitive adhesive on the base sheet should preferably has a thickness in the range from 5 to 100 ⁇ m.
• the blister-preventing effect of the inventive pressure-sensitive adhesive sheet can be exhibited most remarkably when the adhesive sheet is applied to the surface of a shaped article of a synthetic resin from which a trace volume of gases usually emitted over a long period of time.
• synthetic resins are known as gas-­emitting, of which those emitting a relatively large volume of gases responsible for blistering of the adhesive sheets include synthetic resins containing 5% by moles or larger or, in particular, 15% by moles or larger fraction of aromatic units such as styrene-based resins and poly­carbonate resins and acrylic resins such as poly (methyl methacrylate) and the like as well as polyolefin-based resins such as polyethylene before lapse of time after molding.
• synthetic resins containing 5% by moles or larger or, in particular, 15% by moles or larger fraction of aromatic units such as styrene-based resins and poly­carbonate resins and acrylic resins such as poly (methyl methacrylate) and the like as well as polyolefin-based resins such as polyethylene before lapse of time after molding.
• the styrene-based resins above implied include those prepared from a monomer mixture containing 10% by weight or larger or, in particular, 30% by weight or larger amount of styrene monomer such as general-purpose polystyrenes, high-­ impact polystyrenes, copolymers of acrylonitrile, butadiene and styrene, copolymers or acrylonitrile and styrene, copolymers or methyl methacrylate, butadiene and styrene, copolymers of an acrylic rubber, acrylonitrile and styrene, copolymers of acrylonitrile, an ethylene-propylene rubber and styrene, copolymers of acrylonitrile, a chlorinated polyethylene and styrene, Poly(phenyleneoxide) blended with poly styrene such as Noryl resins and the like.
• styrene monomer such as general-purpose
• a presum­able mechanism for the blistering of a pressure-sensitive adhesive sheet applied to the surface of a shaped article of these styrene-based resins is that the styrene monomer in the form of a gas is emitted from the surface of the molded article.
• synthetic resins containing an aromatic-ring-containing monomeric moiety in a molar fraction of 50% or larger or, in particular, 15% or larger may sometimes emit gases responsible for the blistering of adhesive sheets even when no monomeric units of styrene are contained therein because such a synthetic resin readily absorbs moisture or readily absorbs low-molecular sub­stances.
• Synthetic resins having polar groups in the pendant groups to the polymeric chain, such as acrylic resins also behave in a similar manner.
• Polyolefin-based resins such as polyethylene and the like sometimes emit a trace volume of gases before lapse of time after molding although the gas emission therefrom is usually transient and not lasting.
• the pressure-sensitive adhesive sheet of the present invention is also freed from blistering due to such a transient emission of gases from shaped articles of a polyolefin-based resin.
• the blister-preventing effect of the inventive pressure-sensitive adhesive sheet is particularly remarkable when the sheet is applied to the surface of a plate of polycarbonate resin for window pane, plate of poly(methyl methacrylate) resin and shaped article of a styrene-based synthetic resin having high transparency.
• a pressure-­sensitive adhesive sheet is applied and bonded to the surface of a resin plate of polycarbonate or poly(methyl methacrylate) for window pane use with an object of adjustment of sun light transmission or protection of the surface against scratches, occurrence of blisters in the adhesive sheet is particularly detrimental against the beautiful appearance of the plate.
• Blistering in a pressure-­ sensitive adhesive sheet is also very conspicuous when the adhesive sheet is applied as a label to the surface of a shaped article of a styrene-based synthetic resin having high transparency. This problem due to occurrence of blisters is most serious in polystyrene-made cassette cases for magnetic recording tapes.
• the pressure-sensitive adhesive sheet of the invention can be used particularly advantageously on shaped articles of these synthetic resins.
• Viscosity of liquid samples was determined at 23 °C by using a rotational viscometer (Model BM, manufactured by Tokyo Keiki Co.) with a No. 4 rotor rotated at 60 rpm. The values of viscosity are given in centipose.
• Weight-average molecular weight M w was determined by the gel permeation chromatography using a chromatographic apparatus (Model CCP 8000, manufactured by Toso Co.) with tetrahydrofuran as the moving phase taking polystyrenes as] the reference samples.
• Ball-tack was determined according to the J. Dow method specified in JIS Z 0237 and the results were recorded by the largest ball stopped.
• the adhesive sheet was peeled off by pulling at an angle of 180° and the force required for peeling was given in grams per 25 mm width of the sheet.
• the substrate to which the adhesive sheet was bonded was a stainless steel plate
• the measurement was undertaken after lapse of 20 minutes from bonding of the adhesive sheet.
• the substrate was a polycarbonate plate or a polystyrene plate (thickness 2 mm, manufactured by Nippon Test Panel Co.)
• the measurement was undertaken after lapse of 24 hours from bonding of the adhesive sheet.
• the pressure-sensitive adhesive sheet was applied and bonded to the surface of a transparent polystyrene plate shaped by injection molding (thickness 2 mm, manufactured by Nippon Test Panel Co.) and kept standing for 1 hour at 80 °C in a hot air circulation oven to effect accelerated aging before inspection of the occurrence of blisters.
• Measurement was performed by the shearing method at 3.5 Hz by using Rheovibron (Model DDV-II-EP manufactured by Orientech Co.).
• the thus obtained solution of the copolymer had a viscosity of 3000 centipoise and contained 35% by weight of the copolymer which had a weight-average molecular weight of 680,000.
• a pressure-sensitive adhesive sheet was prepared by coating a polyester film having a thickness of 50 ⁇ m with this copolymer solution in a coating amount of 20 ⁇ 2 g/m2 as dried followed by drying in a hot-air circulation oven at 100 °C for 1 minute.
• Example 2 The experimental procedure in each of these examples and comparative examples was substantially the same as in Example 1 except that the formulation of the monomer mixture in the copolymerization reaction was as shown in the following tables. Following tables also summarize the characterization of the copolymers thus obtained and the results of testing of the pressure-sensitive adhesive sheets obtained by using the copolymers.
• the pressure-sensitive adhesive sheet of the present invention is outstandingly free from blistering and exhibits good adhesive bonding strength and holding.
• occurrence of blisters can be effectively prevented in the inventive pressure-sensitive adhesive sheet by forming the adhesive layer with a very unique copolymer even without interposing a gas-permeable layer between the face-stock film and the adhesive layer so that the adhesive sheet is free from undesirable increase in the overall thickness.
• the adhesive layer has good weather-­ability to retain the adhesiveness over a long period of time without losing the excellent adhesiveness.
• the pressure-sensitive adhesive sheet of the present invention can be used quite satisfactorily on molded articles of various kinds of synthetic resins or, in particular, of polycarbonate resins and polystyrene resins.
• the protection and beautiful appearance of the articles can be maintained over a long period of time because the inventive adhesive sheet is free from occurrence of blisters and the adhesive used therein has good weatherability.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Adhesives Or Adhesive Processes (AREA)
• Adhesive Tapes (AREA)
• Laminated Bodies (AREA)

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Citations (2)

• 1988
  • 1988-06-02 JP JP63135989A patent/JPH0798923B2/ja not_active Expired - Fee Related
  • 1988-08-16 AU AU21022/88A patent/AU612394B2/en not_active Ceased
  • 1988-08-17 EP EP88113313A patent/EP0304779B1/fr not_active Expired - Lifetime
  • 1988-08-17 DE DE3851994T patent/DE3851994T2/de not_active Expired - Fee Related
  • 1988-08-24 KR KR1019880010756A patent/KR910004822B1/ko not_active IP Right Cessation

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